DIETETICS 



397 



will not support life, but when added to proteins they enable 

 the animal to do with smaller quantities of the latter. They 

 are thus sometimes termed protein sparers. Their use in 

 diminishing the consumption of proteins is, however, strictly 

 limited. 



Fat Diet. Fats, like carbohydrates, will not support life, 

 because they cannot be used for building up protoplasm ; but, 

 like carbohydrates, they are a source of energy, and they have 

 more than twice the energy value of proteins or of carbo- 

 hydrates. They are thus protein sparers. But experiment 

 has shown that, in spite of their higher energy value, they 

 have not the same power as carbohydrates of sparing proteins, 

 since their digestion and absorption is more difficult. Thus 

 while theoretically 1 grin, of carbohydrate yields 41 Calories 

 of energy, 1 grm. taken in the food, since it is not all absorbed 

 and used, yields 4'03 Calories of energy. But fat, which theo- 

 retically yields 9 '3 on account of its less availability, yields in 

 the body only 8*93 Calories. That is, while carbohydrates yield 

 97 per cent, of their energy, as determined by the calorimeter, 

 fats yield only 92 per cent, of their energy. 



When once absorbed, fats are iso-dynamic with the equivalent 

 amount of carbohydrates. This has been determined by re- 

 placing the carbohydrates in a diet with the equivalent amount 

 of fat. 



A knowledge of the part played by proteins, carbohydrates, 

 and fats in the animal body is the groundwork of the study of 

 Dietetics. 



VI. DIETETICS 



The object of Dietetics is to fit the supply of matter and 

 energy in the food to the requirement of the body under 

 different conditions. 



In all animals the great essentials of a diet capable of 

 maintaining health are: 



1st. That it should be capable of digestion, absorption, and 

 assimilation, i.e. that it should be available. 



2nd. That it should supply the energy required. 



